WMOD00495

• Title: Night Vesus Day Cloud Seeding in Langmuir's Periodic Experiment
• Weather Modification - Doc Type: Report

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Despite widespread commercial seeding during and after the latter
half of the periodic-seeding experiment, Langmuir considered the
first epoch representative of nonperiodic seeding. He expressed
belief that periodicity during the second epoch was accentuated by
seeding timed to coincide with storms but that, without a regular
seeding schedule, the period vacillated over a wide range up to
10 days, suppressing even the normal 7-day component.

The results displayed in table 1 and figure 1 confirm that the
nighttime-seeded cycles did indeed have a stronger 7-day periodicity
of precipitation and associated temperature aloft than did either
the daytime-seeded or the nonperi odi c- seeded cycl es. The differl~nce
is especially clear in the block of contiguous regions immediately
downwind from the seeding site. Outside of this block, the distribu-
tion of probabilities is not inconsistent with chance.

Whether the differences here exhibited were caused by the seeding
remains unsettled. No acceptable theory or supporting evidence has
emerged save that from this unique experiment itself. Many meteor-
ologists consider it inconceivable that the silver iodide smoke
generators at Alamogordo could have had any such effect in the face
of widespread commercial seeding conducted day and night during
cycles 13 through 22. On the other hand, if the periodic-seeding
hypothesis is perhaps true, its importance overshadows that of every
other weather-modification hypothesis so far posited or experiment
so far undertaken. Without access to the calculations that must have
underlain the published data, one can only speculate what more these
might tell. One wonders about the likelihood of such a sequence of
events occurring by chance during a designated 280-day period. The
present results only deepen the mystery.

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